Jason Pattison HBSc thesis abstract

Thesis Title: 
Petrographic Study on the Kenbridge Nickel Deposit

The Kenbridge deposit is a nickel-copper deposit hosted in a pyroxenite intrusion.  The country rock consists of pillowed mafic lavas, while the deposit consists of several gabbroic intrusions followed by a later pyroxenite intrusion, which hosts the mineralization.  The edges of the Kenbridge deposit have been altered to a talc schist.  This was originally believed to have been caused by a shear zone.  However, petrographic observations show that the transition between the pyroxenite to the talc schist is very gradual.  Therefore, it seems more likely the talc schist was created by metamorphic fluid and is an alteration product of the talc schist.  The idea of a metamorphic fluid is supported by the analysis of the variable nickel : copper ratio seen in the deposit.  The secondary ore minerals, which for the most part include chalcopyrite, showed a strong correlation with quartz.  The quartz is a secondary mineral which was brought into the system; therefore, it was concluded that the same method that brought the quartz into the system was also responsible for remobilizing the chalcopyrite.  The possibility that the system could have been altered by a metamorphic fluid is supported through SEM analysis and the creation of theoretical equilibrium reactions for the mineral assemblage using SupCRT92.  The SEM analysis was used to determine the chemical composition of the clinopyroxenes and amphiboles in the deposit.  It was established that metamorphic talc, tremolite and diopside were being created.  These minerals were used in the theoretical equilibrium reactions, and it was determined that first appearance of each of the three minerals represent its own pressure-temperature boundary.  More importantly, these reactions can occur at relatively low pressure and temperature ranges meaning that it is possible for thee reactions to have occurred in the Kenbridge deposit.